(i) Technical Field
The present application relates to an apparatus for output light with wavelength tunable function and a method to determine an oscillation wavelength of a wavelength tunable laser diode.
(ii) Related Art
A plurality of methods are known as a technique to control a wavelength of light output from a tunable semiconductor laser diode (hereafter denoted as LD). A typical wavelength tunable LD has a plurality of portions to tune the wavelength of the light each inherently having a periodical reflection (or gain) peak spectrum. Peak wavelengths in the reflection spectrum attributed to one of portions and those of the gain spectrum attributed to another portion are different from each other. A laser oscillation occurs at the wavelength where the peak wavelength of the reflection spectrum coincides with the peak wavelength of the gain spectrum. Japanese Patent Application Publication No. 7-273400 discloses that a sampled grating (SG) is used as the wavelength selection portion.